This invention relates generally to devices that measure acceleration and more specifically to precision accelerometers such as those used in inertial navigation systems.
The accelerometers used in inertial navigation systems are typically of the pendulous torque-to-balance variety. A typical unit uses a hinged pendulum as the acceleration sensing body. A position sensor produces an error signal when the pendulum begins to pivot away from its desired null position as a result of an acceleration, and this error signal is used by a control circuit to maintain the pendulum in its null position by means of an electrical control signal applied to a torquing device. The magnitude of the electrical control signal is proportional to the acceleration and thus is a measure of the acceleration.
The accelerometer case may either be dry (i.e. filled with dry air or nitrogen) or fluid-filled. The fluid-filled variety results in a simplified pendulum design because of the natural damping of the pendulum resonances provided by the fluid, the ability of achieving a given pendulosity with a larger pendulum assembly as a result of the partial flotation provided by the fluid, and the ease of achieving good damping in the torque-to-balance loop. The disadvantage of using a fluid are the unique requirements that must be accommodated by the manufacturing process. The advantage of the dry units is the elimination of the problems associated with using a fluid. However, dry units require a more exacting pendulum design.
The invention described herein offers a new approach to the design of precision accelerometers in that it utilizes a spinning body as the acceleration sensing element. The sensing element spins in a dry environment, and there are consequently no fluid migration/stratification/compatibility issues which might argue against a long operating life. No electrical connections to the sensing element are required, and the device is radiation hard.